Process for the manufacture of a flexible heat exchanger

ABSTRACT

A method of producing a flexible heat-exchange device including a body having a flexible mats and an internal passageway for heat-carrying fluid, an inlet and an outlet, including placing first and second plastic elastic mats in a mould die having supporting surfaces and recesses around the supporting surfaces, separating the first and second plastic elastic mats by a resilient counterdie, bringing the mould dies together with the first and second plastic elastic mats separated by the resilient counterdie into contact wherein the first and second plastic elastic mats are stretched down around abutment surfaces by deformation of the resilient counterdie and around the support surfaces and down into the recesses so as to obtain local plastic deformations as the mould dies are brought together, placing the second plastic elastic mat over the first plastic elastic mat, and mutually joining the first and second plastic elastic mats to form the body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a flexible heatexchanger for absorbing heat from or delivering heat to itssurroundings, a device for carrying out the method, a flexible deviceproduced in accordance with the method, and the use of a resilient,plastic mat in the production of said heat exchanger.

2. Discussion of the Background

The heat exchanger may conveniently be used, e.g., as an absorber in asolar energy arrangement, or as a heat exchanging element in a heatexchanging system, or for heating water in desalination processes, or inother applications where a fluid is desired to flow separately from thesurroundings for the purpose of absorbing or emitting heat.

The use of flexible rubber material in solar energy absorbing systemshas been found more beneficial than the use of rigid materials, such assteel, aluminium, etc. One advantage is that internal deposits orcoatings in solid form, e.g. salt, lime or crystalline deposits, can beremoved more effectively when cleaning the absorber, since it can bebent and folded during the process, therewith loosening the internaldeposits from the walls of the absorber and enabling the deposits to becrushed and readily washed away.

Known flexible absorbers are typically comprised of two pieces of rubberfabric that are placed one upon the other and then mutually joined alongtheir respective edges, normally by vulcanization. The resultant unit isinflated so as to separate the mantle surfaces of the rubber-fabricpieces and hold said pieces apart while a newly heated moulding toolpresses the fabric pieces together at those positions where it is wishedto join said pieces together, e.g. at positions at which channels willbe formed internally of the absorber.

This provides an inexpensive product in comparison with steel oraluminum absorbers. Despite this, however, the actual production of theabsorber is nevertheless expensive, due to the relatively longvucanizing or curing times required, among other things.

Leakage problems have also occurred at the inlet and outlet of theabsorber, where rigid pipe connectors, normally steel connectors, havebeen vulcanized firmly to the flexible absorber.

A rubber absorber is also relatively heavy and has a limited usefullife, since the rays of the sun which the absorber is intended tocapture tend to decompose the rubber.

Metal and rubber absorbers also have a significant material thickness,which shall be heated together with the fluid. A thick material in theabsorber walls imparts inertia to the absorber when heating from coldconditions, e.g. after a large cloud has passed.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to overcome thesedrawbacks and to provide a flexible heat-exchanger that is light inweight, mechanically strong and that can be produced in a rationalmanner.

This object is achieved with the invention first mentioned above havingthe characteristic features according to one of the accompanyingindependent Claims.

Further developments of the invention are set forth in the followingdependent Claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

Further features of the invention and advantages afforded thereby willbe evident from the following description of a solar energy heatingsystem that includes a flexible heat-exchanging device according to oneembodiment of the invention, said embodiment constituting solely anexample of the invention and having no limiting effect on the inventivescope. To facilitate an understanding of the text, reference signs havebeen included in the Figures of the drawings, in which equivalent orsimilar parts have been identified by the same reference signs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates part of a solar energy heating system in which aninventive device can be used to advantage;

FIG. 2 is a perspective, schematic view showing mutually separated partsof a solar-energy capturing absorber screen;

FIG. 3 illustrates in larger scale part of the screen shown in FIG. 2when mounted;

FIG. 4 is a semi-manufacture of a heat exchanging device according toone embodiment of the invention;

FIG. 5 is a schematic illustration of a production line constructed tocarry out the method; and

FIG. 6 is a sectional view of a heat-exchanger according to oneembodiment of the invention.

FIG. 1 illustrates schematically a number of series-connected absorberpanels 1 that form part of a system for solar heating of a fluid medium.The panels are directed towards the sun in a typical manner, at an angleto the horizontal plane appropriate in respect of the current latitudeon that particular occasion. The fluid flows through the panels whileabsorbing thermal energy, causing the temperature of the fluid to rise.This energy is supplied directly by the rays of the sun and by theambient temperature. The heat is then put to use in other parts of thesystem (not shown), which parts may include an accumulator tank, a heatexchanger or a direct connection to, e.g., a pool or some otherequipment appropriate for the application concerned.

The heating effect achieved with the system is determined essentially byits distance from the sun and the surface area exposed. In theillustrated case, the panels are comprised of module units of standardsurface areas and the heating effect of the system can thus be regulatedby virtue of the number of panels that are connected in the system.

As will be evident from FIG. 2, a panel may include a supporting box 2that has a transparent lid 3. Mounted inside the box is afluid-enclosing device, more specifically a flexible heat-absorbingdevice 4 hereinafter referred to as the absorber. The heat-carryingfluid transports heat as it flows through the absorber 4, this fluidbeing water, aqueous mixtures, or some other suitable fluid, forinstance.

The absorber has two flow openings, an inlet 5 and an outlet 6, and aflow passageway that extends therebetween. In the case of theillustrated embodiment, the passageway spreads across the full surfaceof the absorber and therewith also substantially across the whole of thebottom surface of the box.

In the illustrated, preferred embodiment, the inlet 5 and the outlet 6are disposed in respective diagonally opposite corners of the absorber,and each includes a respective connector device 7. The connector device7 extends through respective sides of the box, for connection tocorrespondingly configured connector devices of adjacent absorbers, orto a conduit that connects the absorber to the remainder of the system.

It will be understood that the inlet and outlet may be given positionsthat are different to those shown, and that several inputs and outputscan be provided in one and the same body 4, in accordance withrequirements relating to the application concerned. The design of theconnector device may be varied and adapted to current requirements. Forinstance, the connector device may include coupling or connectingelements that will enable them to be connected to other systemcomponents quickly, simply and tightly. They can also include absorbersuspension elements in the case of applications in which no box is used,or for fixing or facilitating tightening of the connector device inlead-throughs or transits, for instance.

The box 2 of the illustrated embodiment is rectangular in shape and hastwo mutually parallel end sides and two slightly longer parallel longsides 8. Each of the long sides 8 includes two through-passing openingsfor connection of the absorber to the remainder of the system, oneopening at each end of respective sides. Normally, only two connectionopenings are used, and those openings that are not used are closed withthe aid of sealing plates 10, which are preferably removable. The fouropenings that are available enable the user to place the inlet either atone end or the other of the side provided with said openings, by turningthe absorber 4 upside down in one and the same box.

Turning back to FIG. 1, the series-connected panels of the inventiveheat exchanger are connected to the inlet alternately at the top and atthe bottom of respective panels, this being possible with standard boxesthat have movable cover plates and invertable absorbers. This naturallypresumes that the absorbers 4 have the same material properties withrespect to resistance to solar exposure, imperviousness, and materialstability at both main surfaces, which is the case with the presentembodiment.

The lid 3 is preferably comprised of a transparent insulating material.An example of such a lid is a transparent, plastic lid that has mutuallyseparate air passageways or chambers disposed in one or several layers.An insulating lid of this construction will prevent the leakage of heat,for instance in cloudy conditions. A sealing strip will preferably bedisposed between the box and the lid with the intention of preventingexternal water from leaking into the box, for instance rain orcondensation. The box will also preferably include a drainage hole forevacuating any moisture that may be present.

In one embodiment, illustrated in FIG. 3, the box is provided over itsbottom surface with a bed 11 of insulating material that supports theabsorber 4 and counteracts heat losses through the bottom of the box.The insulation may conveniently have the profiled configuration shown inFIG. 3, wherewith the insulation provides support to the absorber body 4and urges the absorber towards the lid 3 without bringing the body intophysical contact the lid. This design enables the gap between lid andabsorber to be adjusted. In the illustrated embodiment, the depth of thebox is determined by the size of the rigid part of the connector devices7 that are located in the box, these connector devices being coarser, orlarger, than the thickness of the absorber body. In one preferredembodiment, the distance between the lid 3 and the top surface of theabsorber is about 6 mm.

In order to achieve a high degree of efficiency, it is desirable to keepthe height of the flow passage down and, instead, to spread the watervolume over a wide surface area. Trials have shown that a suitable ratiobetween water volume and surface area in absorbers of the present typeis about 1.8 liter per square meter, which corresponds to a water depthof about 1.8 mm. Other water depths are, of course, possible.

In the case of the present embodiment, there has been proposed a patternin which the flow passage has an outer limitation that coincides withthe periphery of the absorber body, and a plurality of spot/dot-likejoints 12 on the absorber 4 inwardly of said periphery, thesespot/dot-like joints 12 resulting in division and spreading of the waterflow. The spot/dot-like joints 12 also prevent bulging of the flowpassage in response to pressure increases in the flexible absorber, suchbulges otherwise resulting in local increases in volume/surface arearatios and lower efficiencies.

The spot/dot-like joints 12 may have different forms, such as round,oval, dog-leg forms, or constitute straight or curved lines. Roundjoints are used in the illustrated case.

When producing the heat-exchanging device used here as an absorber,there is used a flexible, resilient plastic mat into which there ispressed, or embossed, a desired flow passageway pattern. The mat is ableto retain a given form or configuration after plastic deformation. Themat is flexible, watertight and shape-stable when subjected to normalloads under normal operating conditions, e.g. strong sunlight and hightemperatures, both before and after said plastic deformation.

The mat includes at least one thermoplastic polymer sheet, and may alsoinclude a mat-strengthening synthetic carrier. The carrier is preferablycomprised of synthetic fibres, e.g. woven, knitted, warp knitted ornonwoven fabric. It is then covered with at least one thermoplasticpolymer sheet, e.g. a polyurethane sheet. The carrier may be covered ontwo sides with one or more thermoplastic polymer sheets, of which atleast the outermost sheet will conveniently have a dull surface. Thecarrier is chosen in accordance with the desired load-stretchabilityrequired when embossing or depressing the aforesaid pattern.

The carrier used in one embodiment is a woven carrier that is wear andstretch resistant and flexible and pliable. The yarn used in the weaveis a polyester, 280 dtex. In order to enclose and effectively containwater, it is necessary to coat a woven carrier in a manner to close theyarn interstices. The carrier of the present embodiment is thereforecoated with a two-ply polyurethane covering on both sides. The sheets,or layers, may be applied by passing the carrier through a bath and thenadjusting the thickness of the coating sheet by passing the carrierthrough a gap. Other known methods may also be used.

The mat is embossed or depressed by stretching the mat locally,wherewith the deformation becomes plastic when the mat is correctlydimensioned and will retain the embossed pattern. In the aboveillustrated example, the carrier may be dimensioned so as to be thecomponent that is plastically deformed and therewith carry the embossedor depressed pattern.

It is necessary to retain the integrity of the sheets or layers whendepressing or embossing the device, in spite of the locally acting,pronounced surface elongations.

When the carrier has a coarse stitch, a first sheet or layer mayconstitute a so-called priming layer that will ensure that thesubsequent surface layer will be given a denser and smoother surface,such that the combined layer thickness will be more even across thesurface of the mat.

Naturally, it is preferred that a sheet or layer will achieve bothadhesion and sealing.

The thermoplastic layer thus provides a sealing function and enablesmelt-fusion, welding, of the mat, and also contributes towardsprotecting the carrier against the decomposing effect of the sun rays.

In another embodiment of the invention, the mat may be comprised of anon-reinforced thermoplastic foil.

The inventive method of producing the flexible, heat-exchanging devicethat is used here as an absorber comprises the steps of pressing into aflexible mat a pattern that corresponds to the extension of a flowpassageway, placing a second flexible mat over the depressed or embossedfirst mat, and joining the mat together so as to form an absorber body4. The mats may be joined by high frequency, ultrasound, hot air or someother method suitable in respect of the material used, e.g. gluing.

A shape-stable connector device 7 may be provided in the absorber-bodyinlet 5 and in the absorber-body outlet 6, to facilitate connection tothe surrounding system. The mat may also be placed in a mould die thathas support surfaces in an abutment plane and recesses or cavitiesaround said surfaces, wherewith the mat will be stretched from theabutment plane and down into the recesses or cavities when subjected todepression forces.

According to one embodiment, two mirror-image, depressed or embossedmats are joined together to form said body 4, wherewith the jointsjoining said mats are formed by meltfusing together the thermoplasticsurfaces of said mats, these surfaces having undergone plasticdeformation. A stabler joint is obtained when welding at surfaceportions that have not been stretched and where the original thicknessof the material has been retained.

The two mirror-image, patterned mats may be depressed or embossedsimultaneously, e.g. by placing two mats between mirror-image configuredmould dies and separating said mats by a resilient counterdie. The moulddies are then brought together so as to move the mats towards oneanother while separated by the resilient counterdie, wherewith the matsare stretched down around the abutment surfaces by the deformation ofthe resilient counterdie to an extent such as to cause local plasticpattern-forming deformations to occur in the mats.

The shape precision can be improved in the case of large patternedsurfaces, by applying tensile forces to the elastic counterdietransversely to the clamping direction of the mould dies, such as tostretch the resilient counterdie outwards in all directions orthogonallyfrom the axis of the mould-die applying direction.

In accordance with another embodiment, two webs of flexible material areadvanced to a pattern-depressing station at which the mirror-imagepatterns are pressed into the mats. The mats carrying the depressedpatterns are then moved to a mat joining station in which the mats arejoined together, e.g. by high frequency welding. The resultant matcomposite can then be moved to a station in which residual material isremoved, e.g. by punching or stamping.

In one alternative embodiment, subsequent to a pattern pressing process,the resilient counterdie can be removed and the embossing dies broughttogether once again with the mats remaining in their original positions,this time so that the mats will be brought into contact with oneanother, said mould dies being heated sufficiently for the thermoplasticmaterials in the mat surfaces to fuse together, for instance byconnecting the dies to a high frequency unit, or in some other way.

FIG. 5 is a schematic illustration of one embodiment of a device thatcan be used to carry out the method. This device includes two mould dies13 which can be brought into contact with one another and which presenton their mutually opposing surfaces a generally mirror-image pattern inthe form of recesses provided in the die abutment surfaces 14, theserecesses corresponding to the extension of a desired flow passageway.The device also includes two joining tools 15 which can be brought intocontact with one another and which present on their mutually opposingsurfaces generally mirror-imaged patterns in the form of abutmentsurfaces 16 that form the electrodes of the joining tools. Theelectrodes are disposed in a pattern that corresponds to thedelimitations of the flow passageway and that can be connected to a highfrequency unit. A resilient counterdie 17 having generally parallel mainsurfaces can be swung-in between the mould dies 13, or removablyarranged therebetween. The resilient counterdie 17 may be placed in aframe while applying tensile forces in all directions transversely tothe direction in which the dies 13 are brought together.

The apparatus may also include a punch for punching-out the weldeddevice. A punching tool may also be provided for punching-out a blankupstream of or downstream of the mould, therewith enablingshape-standard blanks, preferably provided with guide means in the formof guide holes, for instance, to be placed in the mould and/or thejoining tool.

A production line may include two reels 18 of mat material upstream ofthe mould dies, and means may be provided for advancing the mats inbetween the mould dies 13 in a mat embossing position, and for movingthe embossed mats into position between the mat-joining tools 15. Theproduction line may also include means for advancing the mat compositeto a station that includes a punching or stamping tool or like means,for final trimming of the device/absorber.

The moulding tool and the mat joining tool may also be comprised in oneand the same tool, wherewith the tool abutment surfaces can be connectedcontrollably to a high frequency unit and the resilient counterdiecapable of being swung in between the mould dies when embossing themats. The counterdie is swung away from the mats, when joining the matstogether.

The mould tool will preferably be heated to an elevated temperature inthe embossing process. This can be achieved by passing steam throughchannels in the mould dies, or by providing the mould dies with electricheating elements.

The apparatus may also include a positioning tool for positioning aholder means between the mats in the proximity of the inlet and outletof the device, prior to joining the mats together. This positioningmeans can be connected to the high frequency unit, wherewith theconnector device/devices can be welded firmly to the mats at the sametime as the mats are joined together. This enables a flexibleheat-exchanging device to be produced in a highly rational manner.

FIG. 6 is a schematic illustration of part of an absorber 4 produced inaccordance with the method last described. The illustrated absorber hasbeen cut along the joints, and the connector device 7 has also been cutup in the same plane. The connector device 7 is shown in the form of aslightly conical, rigid tube, e.g., a thermoplastic tube, that has beenjoined to the mat by means of a high frequency welding process.

The free end of the connector device 7 may be provided with any type ofcoupling element suitable for further connection. In one embodiment, thefree end of the connector device includes a collared part which isintended to be received by a similar collared part on an adjacent deviceor conduit, these collared parts having crimped on their inner surface aV-shaped circumferentially exceeding groove, and preferably a packinglocated between their mutually opposing surfaces. The advantage withthis embodiment is that the connections require very little space andtherefore enable the solar collector panels to be placed very closetogether.

What is claimed is:
 1. A method of producing a flexible heat-exchangedevice including a body having a mutually joined plurality of flexiblemats and an internal passageway for a heat-carrying fluid, an inlet andan outlet, comprising the steps of: placing a first plastic elastic matand a second plastic elastic mat in a mould die having supportingsurfaces and recesses around said supporting surfaces, respectively;separating the first and second plastic elastic mats by a resilientcounterdie; bringing the mould dies together with the first and secondplastic elastic mats separated by said resilient counterdie into contactwith one another wherein the first and second plastic elastic mats arestretched down around abutment surfaces by deformation of the resilientcounterdie and around the support surfaces and down into said recessesso as to obtain local plastic deformations as the mould dies are broughttogether; placing the second plastic elastic mat over the first plasticelastic mat; and mutually joining said first and second plastic elasticmats to form said body.
 2. A method according to claim 1, wherein: thefirst and second plastic elastic mats comprise two mirror-image patternshaving local plastic deformations formed by embossing or depressing, andare joined together to form said body; and a plurality of joints isformed at portions of the first and second plastic elastic mats by theplastic deformations.
 3. A method according to claim 2, wherein thebringing step comprises at least one of depressing and embossing thefirst and second plastic elastic mats into two mirror-image patternedmats simultaneously.
 4. A method according to claim 1, wherein thebringing step comprises applying tensile forces to the resilientcounterdie transversely to clamping movement direction of the mould diesto stretch the resilient counterdie outwardly in all directionsorthogonally to an application axis of the mould dies.
 5. A methodaccording to claim 1, further comprising joining edges of said first andsecond plastic elastic mats and effecting internal pattern-producingjoints in one same process.
 6. A method according to claim 2, furthercomprising the steps of: advancing two webs of flexible material to apattern depressing station; depressing the two mirror-image patterns inthe first and second plastic elastic mats; advancing the first andsecond plastic elastic mats thus patterned to a mat joining station; andjoining the first and second plastic elastic mats together.
 7. A methodaccording to claim 2, further comprising the steps of: removing theresilient counterdie after said local plastic deformations formed byembossing or depressing; bringing the two mirror-image dies together;and connecting the two mirror-image dies to a high frequency weldingunit and welding the first and second plastic elastic mats together.